The present invention relates to improvement of a .delta.-doped field-effect transistor, or an atomic planar-doped field-effect transistor, such as GaAs FET, InP FET or InGaAs FET which has a .delta.-doped, or atomic planar-doped, layer in its channel region.
The .delta.-doped, or atomic planar-doped, field-effect transistor has been proposed by Schubert et al. in JAPANESE JOURNAL OF APPLIED PHYSICS, Vol. 24, No. 8 AUGUST, 1985, pp. L608-L610 and in IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-33, No. 5, MAY, 1986, pp. 625-632. Since it is basically a Schottky-gate FET, the maximum usable gate-forward voltage V.sub.Gmax, or the gate-forward turn-on voltage, is as low as about 0.7 eV and a sufficient noise margin cannot be achieved in an LSI employing the atomic planar-doped transistors. Moreover, the short channel effects tend to occur in the proposed atomic planar-doped field-effect transistor.